Cryo before temper

I

itrade

Joined
Jul 3, 2002
Messages
645
(Somebody probably guessed I was going to ask this.)

CPM says to cryo after a first temper. To prevent cracking I presume.

1. Is this really a problem with knife blades?

2. If yes, couldn't you just slow down the process?

* sit in the home freezer (cold)
* suspend in the air space above the LN (very cold)
* lower into the LN (extremely cold)
* soak
* reverse

Steve
 
Steve, if you search last year sometime, there was a very good thread on cyro. That was the most informative thread I've ever read about Cryo tempering for different steels including simple carbon.
 
I seem to remember that Paul Bos goes directly to cryo after quench with martensitic stainless, but includes a temper cycle first on tool and alloy air-hardeners. I don't remember where I read that, so I may be wrong.

I've HT'd about 150 440C and ATS34 blades w/ cryo in dry ice/acetone. I've never tempered first, and I've never had one crack. That doesn't mean I'm doing it right, though. :D I've also left em full hard in the home freezer for two months, warming and monitoring the increase in hardness every week, and never had one crack that way, either.
 
Yes, Paul Bos recommended to me here a few months back to cryo martensitic stainless steels BEFORE temper. You will get greater transformation by doing so. I just put it in there and have had no noticable fractures so far. Just be careful the point does not hit the bottom hard at all. I did loose about 1/32 inch off the point of one once.

RL
 
Roger is right, cryo before tempering gets a bit harder but the risk is greater.
 
I take it this does not apply to carbon steels? I'm pretty much exclusively O1 right now, have always done my weak dry ice/acetone cryo after tempering. Seems to add some value.

Would I do better with O1 deep quenching before the temper?

Thanks,
Dave
 
I continue the quench with dry ice treatment for 8-10 hrs prior to tempering my blades. Mostly I work with D2 and S30V, but also use some A2 and O1. I have never had a blade crack doing it this way.
 
With dry ice you may well easily get away with it. For simple carbon steels I temper once before deep cryo (deep cryo being far below dry ice temp.). I believe, from what I have gathered, it is safer to temper simple carbons before deep cryo. If I was making it for me I'd go for broke but if for a customer I think I would be shy about DEEP cryo before temper. I base this on other peoples advise to me (people I believe in).

RL
 
Dave, I have noticed an increase in hardness with O1 after deep cryo. Before deep cryo ability I used dry ice but at that time did not have in-house hardness testing.

I would suggest that all steels we are apt to make blades of will benefit from cryogenic tempering (cryo treatment to satsify some of us ;)). In fact, if I had the ability to resharpen my drill bits I would cryo them before resharpening. I read somewhere that cryogenic treatment causes a very shallow - a mill or two perhaps - softening at the surface. It was probably me expecting it but I have thought I noticed this will beginning to put an edge on a blade I had cryo-ed.

The last O1 I tested I believe I realized an increase of about 1 HRc cardinal point. I have seen as much as 3 1/2 points with ATS-34. Amazing to me but that is close to what the data sheet told me to expect.

RL
 
the steels like ATS-34 154-CM were designed to be cryo'd
that's why the difference in RC points. the home freezer will take more time value than any benefits realized from it.
I still think it's the time the steel sets that helps the
most in that case.

I cryo on the SS's between tempers
I'd have to see where I saw it but it was recommended the temper
SS right after quenching and the others as in the O1's it didn't matter when you temper, just don't drop it in the floor . :)
 
Dave, in the thread I mentioned, I think the end result was that with carbon steels the cryo was not as critical as with stainless. The carbon steels could be cryo'ed after the first temper cycle with no adverse effects but the stainless needed to be cooled before tempering. I'll do a little searching and see if I can find the thread.
 
You must log in or register to reply here.
Back
Top